This application is based on Japanese Patent Application No. 11-20988 filed on Jan. 29, 1999, No. 11-287476 filed on Oct. 8, 1999, and No. 11-356807 filed on Dec. 16, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel property detecting apparatus for detecting a property of fuel supplied to an internal combustion engine.
2. Description of Related Art
A usual gasoline engine mounted on vehicle are mostly arranged that an intake pipe is equipped with a fuel injection valve. Fuel (gasoline) is injected into an intake port. In this intake port injection system, a part of fuel injected from the fuel injection valve is directly introduced into cylinders. The rest of fuel adheres on an inner surface of the intake port and a surface of an intake valve, and it gradually evaporates and is introduced into the cylinders. Accordingly, the amount of fuel introduced into the cylinders varies according to an amount of evaporating fuel which adheres on the inner surface of the intake port or the like (wet). The amount of evaporating fuel (rate of an evaporation) varies according to the property of fuel, but the property of fuel is not stabilized even among the same kind of fuel. The property is different between makers, and is changed according to the season and sales area even in the same makers fuels. Accordingly, it is necessary to detect the fuel property in order to provide an accurate air-fuel ratio control (fuel injection control) by considering the amount of evaporating fuel.
It is proposed that the fuel property is detected on the basis of each of parameters such as an ability to start, a variation of the rotation and a rising of the rotation as described in JP-A-9-203342.
However, the ability to start, the variation of the rotation and the rising of the rotation are varied according to various factors except for the fuel property. Therefore, it is impossible to detect the fuel property accurately, even if the fuel property is detected by using these parameters, since it is influenced by the various factors except for the fuel property. For instance, in a manual-mission car, there are possibilities of an erroneous detection, because the variation of the rotation and the rising of the rotation varies a lot according to a shift-operation by driver.
As a result, a driveability, a fuel consumption and an emission might become worse, since an accuracy of a correction by the fuel property is lowered.
The present invention was accomplished in consideration of the above-mentioned circumstances, and, the object is to provide a fuel property detecting apparatus for an internal combustion engine that the apparatus is able to detect the fuel property accurately.
In order to achieve the above-mentioned object, the present invention apply to the fuel property detecting apparatus for an internal combustion engine. The injection amount of fuel which is injected from a fuel injection valve or a parameter having a correlation with the injection amount (hereafter generally referred as an injection amount parameter) is calculated by an injection amount parameter calculating means. The combustion amount of fuel which is burnt in the cylinder or a parameter having a correlation with the combustion amount (hereinafter generally referred as a combustion amount parameter) is calculated by means for calculating a combustion amount parameter. Then, the fuel property is detected based on a relationship between the injection amount parameter and the combustion amount parameter.
For instance, a volatility of fuel (ability of evaporation) decreases as the fuel property becomes heavier. The amount of fuel adhered on the inner wall of the intake port or the like (wet amount) is increased and a ratio of the combustion amount to the injection amount of fuel is decreased. Therefore, the relationship between the injection amount and the combustion amount of fuel varies according to the fuel property. Accordingly, it is possible to detect the fuel property accurately, when the fuel property is detected based on the relationship between the injection amount parameter and the combustion amount parameter.
Here, in a case that the combustion amount of fuel is used as the combustion amount parameter, an intake air amount of the internal combustion engine can be detected by an intake air amount detecting means. Air-fuel ratio in exhaust gas can be detected by an air-fuel ratio detecting means. The combustion amount can be calculated by using the detected values. That is, the combustion amount of fuel can be calculated, when the intake air amount and air-fuel ratio in exhaust gas are used, because air-fuel ratio in exhaust gas is defined by the intake air amount and the combustion amount of fuel. Further, it is not necessary to dispose new sensor for detecting the combustion amount parameter, because a usually disposed sensors for air-fuel ratio control can be used for detecting the intake air amount and air-fuel ratio in exhaust gas. Therefore, the costs can be cut down.
A fuel supply excess rate, which is a reciprocal of an air excess rate of a mixture supplied for the internal combustion engine, can be calculated as the injection amount parameter. A combustion fuel excess rate, which is the reciprocal of an air excess rate of exhaust gas, can be calculated as the combustion amount parameter. For instance, a ratio of the combustion fuel excess rate to the fuel supply excess rate is decreased by increasing the wet amount as the fuel property becomes heavier. Therefore, the relationship between the fuel supply excess rate and the combustion fuel excess rate fuel varies according to the fuel property. Accordingly, it is possible to detect the fuel property accurately, when the fuel property is detected based on the relationship between the fuel supply excess rate and the combustion fuel excess rate fuel. In a case that the invention is applied to the system which calculates the combustion fuel excess rate based on an output signal of an air-fuel ratio sensor and controls air-fuel ratio. The invention can simplify a calculating process for the fuel property detection, because the process for calculating the combustion amount parameter is extremely simplified.
Further, the fuel property is detected by comparing an accumulated value of the combustion amount parameter and an accumulated value of the injection amount parameter during a predetermined time. As a result, it is possible to improve a detecting accuracy of the fuel property, because it is possible to reduce an influence of noise and a variation of an operating condition.
Further, the fuel property is detected by comparing an accumulated value of a difference between the injection amount parameter and the combustion amount parameter and the accumulated value of the injection amount parameter during a predetermined time. That is, the difference between the injection amount and the combustion amount is used as a parameter for evaluating the wet amount adhering on the inner wall of the intake port or the like. The ratio of the wet amount to the injection amount increases as the fuel property becomes heavier. Accordingly, it is possible to detect the fuel property accurately, by comparing the accumulated value of the difference between the injection amount parameter and the combustion amount parameter and the accumulated value of the injection parameter during the predetermined time.
Further, it is considered that the wet amount varies in accordance with the operating condition of the internal combustion engine. At least one of the injection amount parameter and the combustion amount parameter or a relationship therebetween or a fuel property detecting criterion are corrected according to the operating condition of the internal combustion engine. As a result, it is possible to carry out the stable detection of the fuel property which is not dependent on the operating condition of the internal combustion engine.
In this case, the wet amount varies according to an intake pressure, an intake air amount, an engine rotational speed, a water temperature or the like, but, is most strongly influenced by the intake pressure. The attention is directed to this point. At least one of the injection amount parameter and the combustion amount parameter or a relationship therebetween or the fuel property detecting criterion is corrected according to the intake pressure. As a result, it is possible to carry out the stable detection of the fuel property which is not dependent on the operating condition of the internal combustion engine by using the intake pressure.
Further, the wet amount is strongly influenced relatively by the engine rotational speed. Therefore, at least one of the injection amount parameter and the combustion amount parameter or the relationship therebetween or the fuel property detecting criterion is corrected according to the engine rotational speed. As a result, it is possible to carry out the stable detection of the fuel property which is not dependent on the operating condition of the internal combustion engine by using the engine rotational speed.
Further, the wet amount decreases as the temperature of the internal combustion engine becomes higher. Therefore, the detecting accuracy of the fuel property is lowered. The variation of the combustion amount according to a difference of the fuel properties is decreased as the temperature becomes higher. In the present invention, it can be used that it is detected whether the internal combustion engine is restarted under a hot condition (hereafter referred as the hot-restart) or not by a hot-restart judging means. The fuel property detection by the fuel property detecting means is prohibited by the fuel property detection prohibiting means upon the hot-restart. That is, the temperature of the inner wall of the intake port or the like has maintained high for a starting of the engine. Then, the wet amount is little in the hot-restart. Therefore, the variation of the combustion amount based on the difference of the fuel properties is little and the detecting accuracy lowers. Accordingly, it is possible to prevent a lowering of the detecting accuracy of the fuel property by prohibiting the detection of the fuel property at the hot-restart.
In both of the heavy fuel and the light fuel, an adhering amount of the injected fuel on the inner surface of the intake port or the like (generating amount of wet) and an evaporating amount of wet are balanced when the temperature of the internal combustion engine rises to a certain level after the starting. The injection amount and the combustion amount of fuel become substantially equal. Accordingly, if there is a difference between the injection amount and the combustion amount of fuel when it rises to such the temperature, the difference can be taken as an error in the system.
This point is taken into consideration. The temperature of the internal combustion engine is detected by an engine temperature detecting means. The relationship between the injection amount parameter and the combustion amount parameter is learned by a learning means when the temperature of the internal combustion engine is not less than a predetermined temperature. At least one of the injection amount parameter and the combustion amount parameter or the relationship therebetween or the fuel property detecting criterion, which are used for detecting the fuel property, is corrected by a learning correcting means by using a learned value which is learned in the learning means. That is, it is possible to learn the system error if the relationship between the injection amount parameter and the combustion amount parameter is learned when the temperature of the internal combustion engine is not less than the predetermined temperature where the injection amount and the combustion amount become substantially equal. It is possible to cancel the system error from the detection of the fuel property by using the learned value. Therefore, it is possible to improve the detecting accuracy of the fuel property.
Further, if a predetermined time has elapsed from the starting, the temperature of the internal combustion engine reaches not less than the predetermined temperature in which the injection amount and the combustion amount of fuel become equal. Therefore, the relationship between the injection amount parameter and the combustion amount parameter is learned by a learning means after an elapse of a predetermined time from the starting of the internal combustion engine. At least one of the injection amount parameter and the combustion amount parameter or the relationship therebetween or the fuel property detecting criterion is corrected by using a learned value. The learned value is learned in the learning means. In such a construction, it is possible to improve the detecting accuracy by canceling the error in the system, similar to the above-mentioned construction.
In order to achieve the above-mentioned object, in the present invention, the attention is directed to a point that the evaporating time constant (evaporating speed) of fuel evaporation are different according to the difference of the fuel properties. The fuel property is detected after the evaporating time constant of fuel is calculated. Specifically, the evaporating time constant of fuel in a fuel transport system model or a physical amount depending on it (hereafter referred as a fuel property parameter) is calculated by the system identification theory by using the fuel transport system model. The model models behaviors of fuel (e.g., a wall surface adherence, an evaporation or the like) in the fuel transport system model until the injected fuel from the fuel injection valve is introduced into the cylinder of the internal combustion engine. The system identification theory is a theory to calculate parameters of transfer functions of a control object by using input and output information of the control object. In the present invention, the control object is the fuel transport system model, the input information is the injection amount of fuel injected from the fuel injection valve, and the output information is the fuel amount actually introduced into the cylinder (hereafter referred as an introduced fuel amount).
In this case, the injection amount as the input information of the fuel transport system model is a known value, because it is calculated in an injection amount calculating means (engine control computer), but introduced fuel amount as the output information can not be detected directly. In the present invention, the attention is directed to that air-fuel ratio of exhaust gas varies as the variation of the introduced fuel amount. Air-fuel ratio of exhaust gas is detected by the air-fuel ratio sensor. The introduced fuel amount is predicted based on air-fuel ratio of exhaust gas.
However, there are delays until the output variation of the fuel transport system model (variation of the introduced fuel amount) appears on the output of the air-fuel ratio sensor. The first is a delay (flow delay) until the gas in the cylinder of the internal combustion engine flows to the air-fuel ratio sensor through the exhaust pipe after an elapse of each stroke such as introduction, compression, expansion and exhaust. The second is a delay (detection delay) based on a response characteristic of the air-fuel ratio sensor. Accordingly, in a case that the output information of the fuel transport system model is predicted based on the output of the air-fuel ratio sensor, it is necessary to synchronize the phases of the input and output information.
In the present invention, the delay until the output variation appears on the output variation of the air-fuel ratio sensor is taken into consideration. The fuel property parameter of the fuel transport system model is calculated based on the injection amount and the output of the air-fuel ratio sensor by a parameter calculating means. The fuel property is detected based on the calculated fuel property parameter by a fuel property detecting means. In such a construction, it is possible to detect the fuel property accurately by using the fuel transport system model. Additionally, number of parts is not increased, because the air-fuel ratio sensor traditionally disposed in the exhaust pipe for the air-fuel ratio feedback control may be used as the air-fuel ratio sensor for predicting the output information of the fuel transport system model. Therefore, it is possible to establish a requirement to reduce the cost.
Further, in a case that the phase of the output information of the fuel transport system model predicted from the output of the air-fuel ratio sensor is synchronized with the phase of the input information, there are two ways. The first is a method for synchronizing the phases of the input and output information by advancing the phase of the predicted output information. The second is a method for synchronizing the phases of the input and output information by delaying the phase of the input information. However, as the former one, the method advancing the phase of the output information predicted based on the output of the air-fuel ratio sensor has a characteristic to amplify a sensor noise. Accordingly, it has a tendency to be influenced by the sensor noise and a disadvantage to need a future value.
In the present invention, it is preferable to synchronize the phase of the input and output information of the fuel transport system model by applying a delay correction to the injection amount. A sensor model can be used. The sensor model models a delay until the output variation of the fuel transport system model appears on the output variation of the air-fuel ratio sensor. In the method to delay the phase of the input information, the sensor noise is not amplified, and the influence of the sensor noise is little. Additionally, the calculating accuracy can be improved, because it is not necessary to use the future value, and it is possible to process by using only the known data.
On the other hand, a combustion fuel amount may be used as a substitute information of the introduced fuel amount, because the introduced fuel amount taken as the output of the fuel transport system model is substantially the same as the amount of fuel burnt in the cylinder (combustion fuel amount). It is possible to calculate the combustion fuel amount based on the amount of introduced air into the cylinder of the internal combustion engine and the output of the air-fuel ratio sensor (air-fuel ratio in exhaust gas). However, the phase of the output of the air-fuel ratio sensor has a delay (flow delay, detection delay) relative to the phase of a detected value of the introduced air amount. This delay is substantially the same as a delay which is modeled by the above-mentioned sensor model.
In the present invention, the injection amount and the introduced air amount are applied the delay correction by using the sensor model. The combustion fuel amount is calculated based on the air-fuel ratio detected by the air-fuel ratio sensor and the delay corrected introduced air amount. The fuel property parameter is calculated by using the delay corrected injection amount and the combustion fuel amount. The introduced air amount is processed by the delay correction by using the sensor model. The phase of the air-fuel ratio detected by the air-fuel ratio sensor and the phase of the delay corrected introduced air amount are synchronized. Therefore, it is possible to calculate the combustion fuel amount accurately.
In this case, it is preferable that the sensor model models the flow delay from the fuel transport system to the air-fuel ratio sensor and the detection delay of the air-fuel ratio sensor. In such a construction, it is possible to construct a sensor model which takes into consideration all factors of delay until the output variation of the fuel transport system model appears on the output variation of the air-fuel ratio sensor. Therefore, it is possible to improve the calculating accuracy of the sensor model.
Further, the flow delay and the detection delay which are modeled by sensor model are set according to the operating condition of the internal combustion engine. That is, The gas flow speed from the fuel transport system to the air-fuel ratio sensor and the time constant of the air-fuel ratio sensor vary according to the operating condition of the internal combustion engine (for instance, engine rotational speed, intake pressure or the like). Therefore, the flow delay and the detection delay which are modeled by sensor model are set according to the operating condition of the internal combustion engine. It is possible to set the proper flow delay and the proper detection delay according to the operating condition of the internal combustion engine.
The input and output of the fuel transport system model (the injected amount and the introduced fuel amount) are maintained constant and not varied when the operating condition of the internal combustion engine is in the steady operating condition. The difference of the evaporating time constant of fuel does not appear on the introduced fuel amount (the output of the fuel transport system model).
In the present invention, it is preferable to detect the fuel property by calculating the fuel property parameter when a transient operating condition is detected by a transient detecting means. The injected fuel amount varies at the transient operating condition and the introduced fuel amount varies far behind it. The difference in the evaporating time constant of fuel which adhered on the inner wall of the fuel transport system appears as a difference of the time constant of the delays on the introduced fuel amount variation. Therefore, It is possible to calculate the fuel property parameter in the fuel transport system model accurately.
Further, the evaporating speed of the adhering fuel on the inner wall of the fuel transport system increases as the temperature becomes higher. The adhering amount of fuel on the inner wall of the fuel transport system is decreased. Therefore, the calculating accuracy of the fuel property parameter is decreased, because the variation of the introduced fuel amount based on the difference of the fuel property (output variation of the fuel transport system model) is decreased as the temperature becomes higher.
In the present invention, it is preferable to determine whether the internal combustion engine is restarted under the hot condition (hereafter referred as the hot-restart) or not. The detection of the fuel property by the fuel property detecting means is prohibited by a property detection prohibiting means when it is in the hot-restart. That is, the variation of the introduced fuel amount according to the difference of the fuel property is little. The temperature of the inner wall of the fuel transport system has been high from just after the starting. The adhering amount of fuel on the inner wall is little when it is in the hot-restart. Therefore, the calculating accuracy of the fuel property parameter is decreased and the detecting accuracy of the fuel property is decreased. Accordingly, it is possible to prevent the deterioration of the detecting accuracy of the fuel property, if the detection of the fuel property is prohibited when it is in the hot-restart.
Further, in a case that the engine is restarted under a cold condition (cold-restart), the temperature on the inner wall of the fuel transport system becomes high as operating time passes away. Therefore, the calculating accuracy of the fuel property parameter is decreased, because the adhering amount of fuel on the inner wall of the fuel transport system is decreased after warm-up is progressed enough.
It is preferable to detect the temperature of the internal combustion engine by a engine temperature detecting means, and to prohibit the detection of the fuel property when the temperature of the internal combustion engine is not less than the predetermined temperature. The detection of the fuel property can be executed at a period. The period is that the adhering amount of fuel on the inner wall of the fuel transport system is relatively a lot after cold-restart, that is, the variation of the introduced fuel amount based on the difference of the fuel property becomes relatively large. Therefore, it is possible to improve the detecting accuracy of the fuel property.
Further, an accumulation of the adhering fuel on the wall surface of the fuel transport system is not enough just after the restart. Therefore, more than a usual amount of fuel is injected to maintain a predetermined air-fuel ratio of exhaust gas. In this time, the input and output appears such that the input is more than a usual amount, and the output is the same as a usual amount. There is a possibility to make an erroneous detection, because this condition is the same as using of fuel having a large evaporating time constant, even under using fuel having a small evaporating time constant.
In the present invention, the detection of the fuel property is prohibited, until the accumulation of fuel adhered on the wall is completed. A start enrichment bears the accumulation of the wall-adhering fuel. Therefore, it can be used that the detection of the fuel property is prohibited until a correction amount of the start enrichment becomes not more than a predetermined value. In such a construction, it is possible to prevent the erroneous detection of the fuel property just after the starting of engine. Further, it is possible to achieve the same effect even to prohibit the detection of the fuel property until the elapsed time from the starting reaches a predetermined value instead of the correction amount of the start enrichment.
Further, fuel is not injected from the fuel injection valve during fuel-cut. In contrast, the air-fuel ratio sensor continues to detect air-fuel ratio during fuel-cut. Therefore, it is possible to detect the fuel property. However, definite erroneous detection of the fuel property is carried out, if the detection of the fuel property is carried out under fuel-cut.
Accordingly, it is preferable to prohibit the detection of the fuel property during fuel-cut and a predetermined time period from an end of fuel-cut. Here, in the predetermined time period from an end of fuel-cut, the detection of the fuel property is also prohibited in the same way as in fuel-cut. The reason of this construction is that the deviation of fuel in the fuel transport system and air-fuel ratio of exhaust gas is not stable just after the end of fuel-cut. The detection of the fuel property is prohibited during the predetermined time period until these become stable. Therefore, it is possible to prevent an erroneous detection of the fuel property during fuel-cut and just after it.
Further, the difference between the evaporating time constant of fuel hardly appears on the introduced fuel amount during an idle operation.
Accordingly, it is preferable to prohibit the detection of the fuel property during the idle operation and a predetermined time period after an end of the idle operation. Here, the detection of the fuel property during the predetermined time period from an end of the idle operation is also prohibited in the same way as in the idle operation. The reason of this construction is that the deviation of fuel in the fuel transport system and air-fuel ratio of exhaust gas is not stable just after the end of the idle operation. The detection of the fuel property is prohibited during the predetermined time period until these become stable. Therefore, it is possible to prevent an erroneous detection of the fuel property during the idle operation and just after it.
Generally, changing the property of fuel mostly happens when the fuel tank is refueled with fuel having different fuel property. Therefore, it is preferable to carry the detection of the fuel property out after refueling.
A refuel detecting means detects whether the fuel tank is refueled or not. A transient operating means forcedly generates a temporary transient operating condition for detecting the fuel property. In this construction, it is possible to execute the detection of the fuel property at every refuels.
As described above, it is preferable to prohibit the fuel property detection during the idle operation. However, in a case that it is left in the idle operation after the starting, warm-up is progressed to increase a temperature in the fuel transport system. Therefore, after that, there is a possibility to be not able to detect the fuel property accurately, even the fuel property detection is executed.
In the present invention, the fuel property is detected by generating the transient operating condition forcedly and briefly by the transient operating means when the idle operation of the internal combustion engine is detected by the idle detecting means. Therefore, it is possible to detect the fuel property accurately during the idle operation even in the case that it is left in the idle operation after the starting.
Here, the injection amount is forcedly varied little to generate the transient operation condition forcedly. Therefore, it is possible to generate the transient operation condition, and to suppress an influence on the driveability.
Further, the injection amount is corrected according to the detection result of the fuel property by an injection amount correcting means. As a result, the injection amount can be a proper amount according to the property of fuel used. Therefore, it is possible to decrease an emission, fuel consumption and a stable driveability which are not dependent on the fuel property.
In the present invention, as shown in FIG. 10, the input information of the fuel transport system model is taken as the injection amount. However, it is possible to constitute a model in which the input information is taken as the supply air-fuel ratio, since the supply air-fuel ratio of the internal combustion engine varies according to a fluctuation of the injection amount.
In this case, a fuel and air transport system model is used. The model models a behavior of the mixture, including fuel injected from the fuel injection valve and introduced air, until the mixture is introduced into the cylinder of the internal combustion engine. The input information of the fuel and air transport system model is taken as the supply air-fuel ratio. The output information is taken as the air-fuel ratio of exhaust gas. Then, the evaporating time constant of fuel or a physical amount dependent thereon is calculated (hereafter referred to a fuel property parameter) based on the supply air-fuel ratio and the output of the air-fuel ratio sensor. In the calculation, it is taken into the consideration that the delay until the air-fuel ratio sensor detects the air-fuel ratio of exhaust gas. As a result, it is possible to detect the fuel property based on the system identification theory by using the fuel and air transport system model in which the input information is taken as the supply air-fuel ratio. The supply air-fuel ratio used as the input information of the fuel and air transport system model is defined by a relationship between the injection amount and the introduced air amount. The supply air-fuel ratio is used as the input information. Therefore, it is possible to improve the detecting accuracy of the fuel property, because the phase of the injection amount and the introduced air amount is synchronized in the fuel and air transport system model.
In the present invention, the air-fuel ratio includes a weight ratio of the air amount A and the fuel amount F (A/F), the air excess rate xcex, the fuel excess rate 1/xcex and various physical amount defined by the relationship between the air amount and the fuel amount. Therefore, the input information of the fuel and air transport system model can be taken as the A/F, the air excess rate xcex or the fuel excess rate 1/xcex.
Further, it is preferable to use a filtering means to remove a low frequency disturbance (drift, offset and trend). The disturbance is contained in the supply air-fuel ratio and the output of the air-fuel ratio sensor used in the calculation of the fuel property parameter. As a result, it is possible to improve the detecting accuracy of the fuel property, because it removes the low frequency disturbance which is a cause of the deterioration of the detecting accuracy of the fuel property.
Further, it is preferable to synchronize the phases of the input and output information of the fuel and air transport system model by correcting the supply air-fuel ratio. The correction of the supply air-fuel ratio is the delay correction using the sensor model modeling the delay until the air-fuel ratio sensor detects the air-fuel ratio in exhaust gas. As a result, the influence of the sensor noise is suppressed, because the noise of the air-fuel ratio sensor is not amplified in the same manner as the above case. Additionally, the calculating accuracy can be improved, because it is not necessary to use the future value, and it is possible to process by using the data which are all known.
Further, it is preferable to learn the time constant of the sensor model by a learning means after warm-up of the internal combustion engine is completed. That is, the detection delay is generated by both of the difference of the fuel property and the time constant of the sensor model before completion of warm-up of the internal combustion engine (during warm-up). However, after completion of warm-up, the generating wet amount and the evaporating wet amount are balanced, because the temperature of the inner wall of the intake port is high to decrease the adhering amount of the injected fuel on the intake port. Therefore, the detection delay by the difference of the fuel property almost disappears. As a result, after completion of the warm-up, it is possible to learn the time constant of the sensor model, because the cause of the detection delay is only the time constant of the sensor model. The time constant of the sensor model is learned and renewed. Therefore, the calculating accuracy can be improved, by canceling the error according to the difference (deviations) and a deterioration with age of the system.